1. Field of the Invention
The present invention relates generally to transferring heat from heat-generating electrical components to heat sinks and, more particularly, to spring spacer assemblies for urging heat-generating electrical components into contact with thermal transfer surfaces of heat sinks.
2. Discussion of the Related Art
Many various products incorporate electrical components that become heated during operation. Commonly used electrical components such as FETs (field effect transitors), for example, generate heat during operation which, if not dissipated, may result in damage to the electrical components. Accordingly, many electrical components may be considered heat-generating electrical components that may be impaired when heated above certain temperatures. Overheating of heat-generating electrical components may cause the electrical components to operate improperly or even fail, with the result that the associated products may also operate improperly or fail.
Given the need to protect heat-generating electrical components from overheating, heat sinks are usually used in conjunction with heat-generating electrical components to absorb and dissipate heat therefrom. Typical heat sinks are made from a thermally conductive material to absorb heat from heat-generating electrical components positioned in contact with thermal transfer surfaces of the heat sinks. Oftentimes the heat sinks are configured with fins or other structure to enhance dissipation of the absorbed heat and thereby maximize the thermal capacity of the heat sinks. Since heat sinks are ordinarily made from metal, the thermal transfer surfaces often comprise thermal interfaces made of thermally conductive but non-electrically conductive material secured on surfaces of the heat sinks. The thermal interfaces electrically insulate the heat-generating electrical components from the metal heat sinks while still promoting thermal transfer from the heat-generating electrical components to the heat sinks.
The degree to which heat sinks are effective in absorbing heat from heat-generating electrical components depends in large parton the integrity of the thermal contact maintained between the heat-generating electrical components and the thermal transfer surfaces of the heat sinks. To maximize heat transfer from the heat-generating electrical components, it is desirable to maximize the surface area of the heat-generating electrical components in contact with the thermal transfer surfaces. In addition, it is desirable for the heat-generating electrical components to be forcefully urged into contact with the thermal transfer surfaces with sufficient force applied at locations conducive to maintaining good thermal contact without causing portions of the heat-generating electrical components to move away from the thermal transfer surfaces.
Various mechanical devices have been proposed for maintaining heat-generating electrical components in contact with thermal transfer surfaces of heat sinks as represented by U.S. Pat. No. 2,740,075 to Walker et al, U.S. Pat. Nos. 4,845,590, 4,922,601 and 4,923,179 to Mikolajczak, U.S. Pat. No. 5,321,582 to Casperson, U.S. Pat. No. 5,363,552 to Coniff, U.S. Pat. No. 5,383,092 to Liberati, U.S. Pat. No. 5,450,284 to Wekell, U.S. Pat. No. 5,466,970 to Smithers, U.S. Pat. No. 5,483,103 to Blickhan et al, U.S. Pat. No. 5,648,889 to Bosli, U.S. Pat. No. 5,991,151 to Capriz, U.S. Pat. No. 6,049,459 to Edmonds et al, U.S. Pat. No. 6,084,773 to Nelson et al, U.S. Pat. No.6,088,226 to Rearick, and U.S. Pat. No. 6,313,995 B1 to Koide et al, and bythe thermal management clips of Thermashield LLC and The Max Clip System(trademark) of AAVID Thermalloy.
As shown by several of the aforementioned references, the heat-generating electrical components may be mounted on printed circuit boards, the heat-generating electrical components typically being disposed along one side of the printed circuit boards with leads of the heat-generating electrical components extending through the printed circuit boards for soldering to the opposite side thereof. The heat sinks are positioned so that the heat-generating electrical components may be placed in contact with the thermal transfer surfaces of the heat sinks. A single printed circuit board may have many heat-generating electrical components mounted thereon, and frequently the heat-generating electrical components are disposed along or near peripheral edges of the printed circuit boards.
Many prior mechanical devices for maintaining heat-generating electrical components in contact with the thermal transfer surfaces of heat sinks operate by forcefully urging the heat-generating electrical components into contact with the thermal transfer surfaces of the heat sinks, but have numerous disadvantages. For example, a single printed circuit board having a plurality of heat-generating electrical components mounted thereon may require a separate mechanical device for each heat-generating electrical component, resulting in additional parts and costs. It is difficult to properly align many prior mechanical devices with the heat-generating electrical components to account for variations in the way that the heat-generating electrical components are mounted to the printed circuit boards. It is difficult to disassemble or remove many conventional mechanical devices from the printed circuit boards, the heat sinks and/or the heat-generating electrical components such that many devices are essentially non-removable or permanent, thereby limiting future repair or replacement. Many mechanical devices for maintaining heat-generating electrical components in contact with the thermal transfer surfaces of heat sinks require highly customized heat sinks to accommodate the devices so that the use of less costly heat sinks is precluded. In addition, it is common for conventional mechanical devices to require larger size heat sinks in order to mount the mechanical devices, and the need for larger heat sinks increases the cost and size of the associated products. Products in which conventional mechanical devices are used to maintain heat-generating electrical components in contact with the thermal transfer surfaces of heat sinks will generally have a larger size footprint due to the presence of the mechanical devices. Where the mechanical devices comprise clips, the clips ordinarily extend beyond the periphery of the printed circuit boards, resulting in a larger footprint. Larger size footprints may be unsuitable for many applications, such as those in which the associated products must fit on pre-fabricated, standard size mounting panels and assemblies. Clips and other prior mechanical devices may also significantly increase the height or depth of the assemblies formed by the printed circuit boards, the heat sinks and the clips or other mechanical devices, and such size increases are usually undesirable.
Many conventional mechanical devices provide inferior thermal contact between the heat-generating electrical components and the thermal transfer surfaces of the heat sinks due to insufficient forces applied to the heat-generating electrical components, the application of non-uniform forces and/or the application of forces at undesirable locations causing portions of the heat-generating electrical components to move away from the thermal transfer surfaces. Examples of mechanical devices having this drawback are those comprising screws or other threaded fasteners extending through the heat-generating electrical components into the heat sinks and capable of being tightened to urge the heat-generating electrical components into contact with the thermal transfer surfaces of the heat sinks. The screws or other threaded fasteners, one of which is needed for each heat-generating electrical component, add to the cost and labor intensiveness of assembly. Furthermore, consistent, repeatable torque control of screws and threaded fasteners is difficult to attain. Under-tightening or under-torqueing the screws or other threaded fasteners results in insufficient force being applied to the heat-generating electrical components with concomitant poor thermal contact. Screws and other threaded fasteners are also susceptible to being over-torqued or over-tightened, potentially damaging the heat-generating electrical components and/or causing portions of the heat-generating electrical components to pivot, tilt or otherwise move out of contact with the thermal transfer surfaces. Undesirable tilting, pivoting or moving of the heat-generating electrical components out of contact with the thermal transfer surfaces as a result of non-axial or substantially non-axial force or pressure may also occur in clips and other types of prior mechanical devices in addition to those employing screws or threaded fasteners through the heat-generating electrical components. It is also possible with many prior mechanical devices for the heat-generating electrical components to move out of thermal contact with the thermal transfer surfaces in response to vibration, thermal expansion and/or thermal contraction, such that thermal contact is not continuously maintained. Many prior mechanical devices are susceptible to becoming loose and causing thermal contact to be impaired.
It is seen from the above that there is a need for a mechanical device for urging one or more heat-generating electrical components mounted on a printed circuit board into contact with a thermal transfer surface of a heat sink in a manner maximizing the surface area of the one or more heat-generating electrical components maintained in contact with the thermal transfer surface while ensuring good thermal contact along the entire surface area to maximize heat transfer. There is a further need for a mechanical device which is easily assembled to a printed circuit board and a heat sink to bias one or more heat-generating electrical components on the printed circuit board into contact with a thermal transfer surface of the heat sink, and is also easily disassemblable from the printed circuit board and heat sink. An additional need exists for a single mechanical device capable of urging a plurality of heat-generating electrical components on a printed circuit board into contact with a thermal transfer surface of a heat sink while conserving parts, labor and cost. There is also a need for a mechanical device for being assembled with a printed circuit board and heat sink to urge one or more heat-generating electrical components on the printed circuit board into contact with a thermal transfer surface of the heat sink without increasing the peripheral size or footprint for the assembled printed circuit board and heat sink.
Accordingly, it is a primary object of the present invention to overcome the aforementioned disadvantages of prior mechanical devices used to maintain heat-generating electrical components in contact with thermal transfer surfaces of heat sinks.
Another object of the present invention is to maximize the surface area of a heat-generating electrical component maintained in good thermal contact with a thermal transfer surface of a heat sink.
A further object of the present invention is to optimize thermal contact between a heat-generating electrical component and a thermal transfer surface of a heat sink.
An additional object of the present invention is to urge a surface of a heat-generating electrical component into contact with a thermal transfer surface of a heat sink with more uniform pressure along the surface of the electrical component.
The present invention has as another object to provide a spring spacer assembly for urging a heat-generating electrical component on a printed circuit board into contact with a thermal transfer surface of a heat sink without increasing the footprint of the printed circuit board and/or heat sink.
It is also an object of the present invention to simplify assembly of a printed circuit board and heat sink to a spring spacer assembly used to urge one or more heat-generating electrical components on the printed circuit board into contact with a thermal transfer surface of the heat sink.
Moreover, it is an object of the present invention to enhance the reliability of heat-generating electrical components by optimizing thermal management of the heat-generating electrical components.
Still another object of the present invention is to provide an individual spring spacer assembly capable of urging a plurality of heat-generating electrical components on a printed circuit board into contact with a thermal transfer surface of a heat sink in response to the spring spacer assembly being fastened to the heat sink through the printed circuit board.
The above-mentioned objects are achieved independently and in combination, and it is not intended that the present invention be construed as requiring two or more objects to be combined unless expressly required by the claims.
Some of the advantages of the present invention are that the spring spacer assembly can be designed for any number of heat-generating electrical components; the spring spacer assembly does not include any parts which penetrate or pass through the heat-generating electrical components; the spring spacer assembly comprises a minimum number of simple parts which may be assembled to a heat sink with conventional threaded fasteners or screws; the spring spacer assembly can be used with various types of heat-generating electrical components and, in particular, with FETs; the force exerted by the spring spacer assembly on a heat-generating electrical component can be selectively varied by varying the spring strength and/or deflection; the thermal transfer surface of the heat sink may comprise a conventional thermal interface secured on a surface of the heat sink; conventional printed circuit boards, heat sinks and thermal interfaces can be minimally modified with appropriate holes or apertures for use with the spring spacer assembly; the spring spacer assembly confines the printed circuit board and ensures proper spacing of the printed circuit board in relation to the heat sink; proper force on the heat-generating electrical components is established consistently and repeatedly to ensure good quality control; tilting of the heat-generating electrical components is avoided; alignment of the spring spacer assembly with the heat-generating electrical components is facilitated; alignment of the spring spacer assembly with the heat-generating electrical components is achieved even where variations occur in the way the heat-generating electrical components are mounted; maintenance and repair are simplified since the spring spacer assembly is easily disassembleable or removable; and loss of good thermal contact due to vibration, thermal expansion and/or thermal contraction is avoided.
These and other objects, advantages and benefits are realized with the present invention as generally characterized in a spring spacer assembly for maintaining thermal contact between a thermal transfer surface of a heat sink and a heat-generating electrical component mounted on a printed circuit board between the printed circuit board and the thermal transfer surface. The spring spacer assembly comprises a spring spacer including a face defining a fixation segment and a deflectible finger extending from the fixation segment, a spacer extending from the fixation segment along a first side of the face, and a protrusion extending from the finger along the first side of the face. The spacer is insertable through a corresponding hole in the printed circuit board for abutment with the thermal transfer surface with the printed circuit board disposed between the thermal transfer surface and the face. The protrusion is insertable through a corresponding hole in the printed circuit board to contact the heat-generating electrical component and cause deflection of the finger in a direction away from the thermal transfer surface as the spacer is positioned in abutment with the thermal transfer surface. A fixation element of the spring spacer assembly secures the face to the heat sink with the spacer secured in abutment with the thermal transfer surface. When the spacer is secured in abutment with the thermal transfer surface, the deflected finger is biased toward the thermal transfer surface so as to apply a force against the heat-generating electrical component, via the protrusion in contact therewith, in the direction of the thermal transfer surface. The force applied by the deflected finger urges the heat-generating electrical component into thermal contact with the thermal transfer surface.
In one embodiment, the spring spacer comprises a spacer member defining the face and also comprises a separate spring disposed over a second side of the face, opposite the first side, for biasing the deflected finger toward the thermal transfer surface. Where a separate spring is provided, the finger itself may be resiliently biased toward the thermal transfer surface such that some of the spring force is applied by the spacer member. In another embodiment, the spacer member applies the entire force needed to urge the heat-generating electrical component into thermal contact with the thermal transfer surface without a separate spring.
The face is disposed in an undeflected configuration prior to the protrusion contacting the heat-generating electrical component and is moved to a deflected configuration in response to the protrusion contacting the heat-generating electrical component as the spacer is placed in abutment with the thermal transfer surface. In the undeflected configuration, the finger is in an initial position relative to the fixation segment, and in the deflected configuration the finger is moved relative to the fixation segment from the initial position in a direction away from the thermal transfer surface. The finger may be co-planar with the fixation segment in the undeflected configuration and may extend at an angle to a plane of the fixation segment in the deflected configuration. The length of the protrusion may be selected to obtain a predetermined amount of deflection of the finger in accordance with the thickness of the portion of the heat-generating electrical component contacted by the protrusion. The finger may extend laterally from the fixation segment to a tip, and the protrusion may be disposed at or near the tip to facilitate deflection of the finger. The finger may have various surface configurations including triangular and rectangular surface configurations. The spacer and protrusion can have various configurations.
The spring may be disposed in an undeformed condition prior to deflection of the finger and moved to a deformed condition by the finger as it is deflected. The spring may have a surface configuration matching or corresponding to the geometric shape of the surface configuration of the face. The spring may comprise a fixation segment disposed over the fixation segment of the face and a finger disposed over the finger of the face. The spring may be planar in the undeformed condition, with the finger of the spring being deflected correspondingly by the finger of the face so that the finger of the spring is disposed at an angle to the fixation segment of the spring in the deformed condition. Deflection of the finger of the spring is used to impart a biasing force against the finger of the face having its protrusion in contact with the heat-generating electrical component, since the spring is biased toward its undeformed condition.
The fixation element may comprise a screw for threaded engagement in a threaded hole of the heat sink. A passage may extend through the face and the spacer for receiving the fixation element therethrough. Where a spring is disposed over the second side of the face, the fixation element may extend through the spring. The spring spacer assembly may comprise a fixation member for being secured over the fixation segment along the second side of the face, and the fixation element may extend through the fixation member so that the fixation member is tightened against the fixation segment when the fixation element is engaged with the heat sink. The spring disposed over the second side of the face may be disposed between the face and the fixation member, and the fixation element may pass through the spring.
The face can have a fixation segment of any desired length and width with any desired number of fingers extending from the fixation segment along its length and/or width in accordance with the number of heat-generating electrical components between the printed circuit board and the thermal transfer surface of the heat sink. Any desired number of spacers can be provided along the length and/or width of the fixation segment, and a fixation element can extend through each spacer into engagement with the heat sink. The spring may have a finger for each finger of the spacer member. Accordingly, an individual spring spacer assembly may be used to maintain a plurality of heat-generating electrical components in thermal contact with a thermal transfer surface of a heat sink.
The present invention is further generally characterized in a thermally protected electrical component system comprising a heat sink having a thermal transfer surface, a printed circuit board spaced from the thermal transfer surface and having a heat-generating electrical component mounted thereon between the thermal transfer surface and a first side of the printed circuit board, and a spring spacer assembly secured to the heat sink via the printed circuit board. The printed circuit board has an aperture therethrough in alignment with the heat-generating electrical component and also has a hole therethrough. The spring spacer assembly comprises a face disposed over a second side of the printed circuit board, opposite the first side, and defining a fixation segment and a deflectible finger extending from the fixation segment. A spacer extends from the fixation segment through the hole and is secured in abutment with the heat sink. The protrusion extends through the aperture in the printed circuit board into contact with the heat-generating electrical component The finger is spring biased toward the thermal transfer surface to apply a force against the heat-generating electrical component, via the protrusion in contact therewith, to urge the heat-generating electrical component into thermal contact with the thermal transfer surface.